The invention relates generally to the field of power systems. In particular, the invention concerns an evaporatively cooled rotor for a gas turbine.
Internal combustion engines, such as gas turbine engines, utilize a working fluid that at all times remains gaseous. During combustion, however, the working fluid does change its composition, from air and fuel to combustion products. The stochiometric optimal temperature for effecting this change is in the neighborhood of 4000 degrees Farenheit.
A conventional gas turbine engine includes a compressor, a combustion chamber, and a turbine made up of an arrangement of stators and rotors. Each of the rotors includes blades and a supporting disc. The walls of the combustion chamber, the stators, and the rotor blades all come into contact with the hot combustion gases and, due to metallurgical concerns, are unable to withstand the temperatures discussed above. As a result, conventional gas turbine engines operate at temperatures of at most only 2800 degrees Fahrenheit and utilize various cooling techniques to lower the temperature of engine parts even further. This results in low power per unit of airflow and low fuel efficiencies, relative to those possible with near-stoichiometric combustion.
Cooling of the stationary stators and combustion chamber walls by evaporative means such as are proposed here is relatively straight forward and various effective techniques are readily available. Due to the speed at which the rotors rotate, however, it is especially difficult to cool the rotor blades.
Today, many engines utilize air cooling to maintain the temperature of metal parts in the combustor and turbine substantially below that of the working fluid. For example, at the conventional operating temperatures noted above, air cooling can be utilized to limit the temperature of the rotor blades to around 1800 degrees Fahrenheit.
As stated, though, due to metallurgical concerns firing temperatures are still well below those corresponding to optimum stoichiometric conditions for combustion. Accordingly, the efficiencies and power densities attained with known engines are significantly below those which are potentially achievable with turbine inlet temperatures corresponding to stoichiometrically ideal combustion conditions.
Various approaches have been proposed for utilizing internal fluid cooling to more effectively cool engine parts such as combustion chamber walls and turbine rotors and stators. In the case of rotor blades, some approaches have involved the internal circulation of cooling fluid from the root of a rotor out through the tip of the rotor blade. Another approach has been to utilize a closed cycle cooling system in which cooling fluid occupies a portion only of an internal cavity in the blade. The physical properties of the cooling fluid are such that it is vaporized in certain regions of the internal cavity by reasons of the temperature prevailing in those regions during normal operation of the engine.
A significant problem with such closed cycle cooling of rotors is the difficulty associated with distributing the liquid phase of the cooling fluid over the walls of the internal cavity of the rotor. Without a substantially even distribution of the cooling fluid, uniform cooling of the rotor blade cannot be achieved.
It is an object of the invention, therefore, to provide an internal combustion engine in which combustion temperature is maintained at a level based on stoichiometric, rather than metallurgical, considerations for maximum performance and efficiency. It is another object of the invention to provide an internal combustion engine wherein higher combustion temperatures can be achieved while maintaining material temperatures at levels at least as low as those associated with known engines. Another object of the invention is to provide a gas turbine engine utilizing closed cycle evaporative cooling for the engine's moving parts. Still another object is to provide a rotor for use in a turbine of such an engine.